1. Field of the Invention
The present invention relates to a battery pack and a manufacturing method thereof.
2. Description of the Related Art
Generally, unlike a primary battery, a secondary battery can be charged and discharged, and is formed in a battery-pack. The secondary battery has been widely used as a power source for mobile electronic appliances such as a cell phone, a notebook computer, a personal digital assistant (PDA), a camcorder, etc.
In particular, because of its relatively high operation voltage and energy density per part weight, a lithium secondary battery has been used in the mobile electronic appliances field.
A lithium secondary battery pack generally includes a bare cell having an electrode assembly. The electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator between the positive electrode plate and the negative electrode plate are wound. In addition, the battery pack includes a built-in case that seals the electrode assembly while exposing a positive terminal of the positive electrode plate and a negative terminal of the negative electrode plate. The battery pack is completed by sealing the outer surface of the bare cell with an outer case in a state where a safety device such as a protective circuit is mounted on an outer surface of the bare cell.
A polymer battery pack is another example of a battery pack and includes a core pack formed by connecting a protective circuit member to a pouch-type bare cell, and a case that covers the core pack. Here, the pouch-type bare cell refers to a lithium-polymer battery where an electrode assembly and a polymer electrolyte are contained within a pouch composed of casted polypropylene, aluminum, and/or nylon (and/or polyethyleneterephthalate). For reference purposes, such a polymer battery pack (or lithium-polymer battery) is distinguished from a non-polymer battery pack (or lithium ion battery) that uses liquid electrolyte.
In such a polymer battery pack, a pouch that constitutes a bare cell is mainly an aluminum foil type bare cell, and thus such a pouch is easily damaged by an outer shock, and the reliability of such a cell is relatively low. Accordingly, the polymer battery pack may include an outer case that covers the core pack, in order to protect the core pack, in which a protective circuit member is attached on the pouch-type bare cell, from the outside.
In more detail, a conventional battery pack includes a bare cell that can be charged and discharged; a protective circuit board that is combined electrically to the bare cell, that controls the charge and discharge, and that blocks (or protects) the circuit from being over-charged or over-discharged; and a resin-molding part, which is formed by a hot-melting method in a way that can be mounted to an outside set, and that does not separate the protective circuit board from the bare cell.
The conventional battery pack, where a whole case is formed by a resin-molding part, uses a hot-melting resin in order to form the resin-molding part. However, the outer appearance of the battery pack formed by a hot-melting resin can exhibit relatively high outer appearance defects because of the characteristic of the materials used in the hot-melting resin. For example, bubbles can be generated in the hot-melting resin. In addition, the outer appearance defect rate (or defect rate of the outer form) is even higher at a portion of the outer case of the battery pack formed by the resin-molding part having a relatively complicated shape, e.g. at a portion of the outer case where a protective circuit board is formed.